1. Field of the Invention
This invention relates to a process which can be used for any combination of stiffening, thermally bonding, embossing or shaping sheet or strip materials. Specifically, the invention relates to a process and apparatus in which embossing design or percentage of bonded area may be almost continuously varied during the ongoing production operation.
2. Description of the Prior Art
As is common knowledge, processes and apparatuses of this type have calender rollers which are used to process and machine sheet materials, such as fiber matting. The calender rollers are used to stiffen, produce decorative patterns or thermally bond the sheet material. In this process, one or both rollers may be heated and additionally, one or both rollers can be provided with a surface area design which is formed by raised, discrete points extending over the calender rollers.
The fiber matting is introduced, under pressure, into a gap formed between the spaced apart rotating calender rollers. The extent or degree of overlap between opposing pairs of raised, discrete points, creates an embossing surface. This surface determines the pattern of the finished sheet or fiber matting which results in a bonding or stiffening of the embossed surfaces.
A process as described above was made public by West German patent DE OS 21 07 887 and utilizes two calender rollers. Each roller exhibits a surface area design composed of raised, discrete points which are heated and insulated. According to the process disclosed, the calender rollers are rotated in such a way that the raised points on each roller overlap at least to some degree.
Because of the surface area design of the calender rollers used in the prior art process, a very specific embossing pattern results on the fiber matting or sheet. The fiber matting, accordingly, possesses a very specific embossed surface, which is indicated by a percentage.
If it is intended that the end product be a soft material, a relatively small embossing surface is sufficient. For more durable materials, a larger embossing surface must be selected. Therefore, depending on what is required from the desired end product, it is necessary to utilize different calender rollers corresponding to the embossing surface desired. Consequently, the prior art calender rollers must be replaced when a different embossing surface is required.
The disadvantage in replacing calender rollers to achieve different embossing surfaces is easily recognized. The process of changing rollers requires a great deal of time and results in longer production downtime. This is because calender rollers are quite heavy and a great deal of time is needed to replace them. In order to eliminate this downtime and enable a more rapid replacement of rollers to achieve different embossing surfaces, the industry has aleady begun equipping several individual calender stands with two calender rollers each. Each calender stand is outfitted with a smooth roller and an embossed roller, each having a different surface area design. In so doing, the different embossing rollers can be put into operation relatively quickly, as needed. Even this solution is very time-consuming because of the large number of embossing rollers involved and also because these numerous calender stands require a significant amount of working space.
For this reason, the most commonly used method is still to stop production whenever a change in the embossing pattern or embossing surface is necessary and to carry out the time-consuming calender roller replacement.
The present invention overcomes these problems by providing a process as well as an apparatus capable of implementing the process, which enables rapid and consequently extremely economical embossing design change. With this process one can quickly change from an initial embossing design to another desired design or to another embossing surface percentage. This process and apparatus also enables an almost continuous variation of the embossing surface percentage during ongoing production operations.
In summary, the present invention, as it relates to the thermal bonding of fiber matting materials, for example, provides the following advantages over the prior state of the art:
(a) Machine downtime incurred in replacing embossing surfaces is significantly reduced or eliminated.
(b) The specified values for the consistency of finished matting can, through gradual adjusting of the embossing area during thermal bonding, be safely maintained during production. This can be done despite variations in raw materials and/or variations in fiber orientation.
(c) Investment costs for embossing rollers, when several embossing patterns are used, are drastically reduced. If, for example, three different embossing patterns are used, traditional technology requires eight rollers, including replacement rollers. When the present invention is used, only four rollers, including replacement rollers, are required.
(d) Lower costs for embossing rollers because, when two "patterned" rollers are used (rather than one smooth), the etching depth of each roller need only be half as deep.
(e) Matting that has been thermally bonded through application of the invention has a distinctly softer "feel". This is because "secondary bonds" are not present. These bonds develop as a result of the complete contact of one side with a smoothing roller which is representative of current state of the art.